The successful calving of the cow and its transition to lactation are two critical keys to cattle farm productivity. For the farmer to achieve their productivity goal there are two critical disease challenges that must be overcome:
Parasitism in the cow—The energy demand of the unborn calf can place the pregnant cow under great stress. As a result body condition suffers and the immune system becomes less effective at warding off infection. One of the major types of infection is parasitism. Usually adult cattle have a high degree of immunity to parasite infection but this is not the case during the calving period.
To help the cow overcome any acquired parasite burden farmers may treat cows during pregnancy with anthelmintics. These products are drugs designed to kill resident worm populations, and in some cases, prevent further infection for a period of time. Historically drugs such as levamisole, oxfendazole, fenbendazole, albendazole, abamectin and ivermectin have been used. These are administered in oral, injectable or topical form. However they have the disadvantage that there is a risk of residues of these anthelmintic drug being present in the milk of the cow after calving has occurred and lactation has commenced. In some countries, such anthelmintics cannot be used to treat animals whose milk is to be used for human consumption, while in other countries, the treatment period before lactating commences must be in excess of 60 days.
Scours in the Calf—The most common cause of calf morbidity in the neonatal period is diarrhea. The major cause of this diarrhea is the presence of scour-causing bacteria and viruses, including Escherichia coli, Clostridium perfringens, Rotavirus and Coronavirus; often in combination and/or with other bacteria, viruses and intestinal parasites.
Viruses—Rotavirus infection is the most common viral cause of diarrhea in calves. Groups A and B rotavirus are involved, but group A is most prevalent and clinically important and contains several serotypes of differing virulence. Rotavirus replicates in the mature absorptive and enzyme-producing enterocytes on the villi of the small intestine, leading to rupture and sloughing of the enterocytes with release of virus to infect adjacent cells. Rotavirus does not infect the immature cells of the crypts. With virulent strains of rotavirus, the loss of enterocytes exceeds the ability of the intestinal crypts to replace them; hence, villous height is reduced, with a consequent decrease in intestinal absorptive surface area and intestinal digestive enzyme activity.
Coronavirus is also commonly associated with diarrhea in calves. It replicates in the epithelium of the upper respiratory tract and in the enterocytes of the intestine, where it produces similar lesions to rotavirus but also infects the epithelial cells of the large intestine to produce atrophy of the colonic ridges.
Bacteria—E. coli infection is the most important bacterial cause of diarrhea in calves; at least 2 distinct types of diarrheal disease are produced by different strains of this organism. One type is associated with enterotoxigenic E. coli, which has 2 virulence factors associated with the production of diarrhea. Fimbrial antigens enable the bacteria to attach to and colonize the villi of the small intestine. Strains present in calves most commonly possess K99 (F5) or F41 fimbrial antigens, or both. These antigens are the focus of immunologic protection. Enterotoxigenic E. coli also express a thermostable, nonantigenic enterotoxin (Sta) that influences intestinal ion and fluid secretion to produce a noninflammatory secretory diarrhea. Diarrhea in calves and lambs also has been associated with enteropathogenic E. coli that adhere to the intestine to produce an attaching and effacing lesion, with dissolution of the brush border and loss of microvillus structure at the site of attachment, a decrease in enzyme activity, and changes in ion transport in the intestine. These enteropathogens are also called “attaching and effacing E. coli.” Some produce verotoxin, which may be associated with a more severe hemorrhagic diarrhea. The infection most frequently is in the cecum and colon, but the distal small intestine can also be affected. The damage in severe infections can result in edema and mucosal erosions and ulceration, leading to hemorrhage into the intestinal lumen.
Clostridium perfringens types A, B, C, and E produce a variety of necrotizing toxins which cause a rapidly fatal hemorrhagic enteritis in calves. The disease in calves is rare and usually sporadic.
At present, anthelmintic treatment of pregnant cows is achieved with a dedicated anthelmintic formulation (oral, topical and/or injectable). These formulations currently do not contain any form of vaccine treatment able to provide protection to the new born calf. However, a number of scours-only vaccines are currently marketed for use in cattle. These vaccines are generally classified as inactivated, referring to the fact that the vaccine contains killed virus or bacterial components. Typically these vaccines will contain inactivated strains providing protection from a number of the causative elements of scouring (rotavirus, coronavirus, E. coli, clostridial diseases) Cows are treated with the vaccine usually by deep intramuscular injection with a dose of between 2-5 mL. This treatment as an annual booster soon before calving provides a strong increase in antibodies in the colostrum available to the calf immediately after calving. Calves fed colostrum from vaccinated cows during the first two to four weeks of life have been demonstrated to have:                Reduced incidence of scours caused by rotavirus and coronavirus        Reduced shedding of virus due to infection with rotavirus or coronavirus        Reduced severity of diarrhea caused by E. coli.         
Typical scour vaccines of this kind available in the United States include:
GUARDIAN® (Schering-Plough). This is a multi-component vaccine which includes Escherichia coli K99 antigen, two inactivated coronaviruses, two G-types of inactivated rotaviruses, and bacterin-toxoid from Clostridium perfringens Types C and D. GUARDIAN is recommended for use in pregnant cattle as an aid in the prevention of neonatal calf diarrhea caused by enterotoxigenic E. coli pilus type K99, bovine Group A Serotype G6 rotaviruses, enterotoxemia caused by C. perfringens Types C and D, and as an aid in the control of neonatal calf diarrhea caused by bovine coronaviruses.SCOURBOS 9 (Novartis). Another multi-component vaccine which includes, four different E. coli strains, three inactivated rotaviruses (serotypes G10, G6 and G8), inactivated Coronavirus and Clostridium perfringens Type C bacterin-toxoid.SCOURGUARD (Pfizer). A combination of inactivated bovine rotavirus (serotypes G10, G6), inactivated coronavirus, and E. coli K99 bacterin-toxoid.
For all three vaccines, a 2 mL dose is administered via deep intramuscular injection. There is no milk withholding period applied to any of the treatments. Treatment programs rely on a two dose treatment schedule in the first year of use, then a single annual booster dose given each year prior to calving. The recommended time at which the treatments should be given (in weeks prior to calving) is outlined in Table 1.
TABLE 1First Year of TreatmentAnnual booster(treatment time in(treatment time inweeks prior to calving)weeks prior toInitial DoseBooster Dosecalving)GUARDIAN12weeks9-6weeks7-5weeksSCOURBOS16-8weeks4weeks10-8weeksSCOURGUARD9-6weeks6-3weeks6-3weeks
The difference in treatment times is explained by the claimed relative effectiveness of the vaccine antigens used with each vaccine. However it should be noted that the closest number of weeks to calving in which the three treatments are recommended to be administered is 5 weeks (GUARDIAN annual booster), 4 weeks (SCOURBOS Booster Dose) and 3 weeks (SCOURGUARD Booster Dose and Annual Booster). In the best case this is only 35 days from calving while in the worst case it is 21 days from calving.
Attaining high levels of antibody in the colostrum through the use of potent vaccines has proven extremely effective in preventing calf scours. The most effective vaccination program is one in which the level of antibodies in the cows system peaks at or just prior to calving, providing maximum protection to the calf via the colostrum. For this purpose there is a requirement that the annual booster vaccine be given reasonably close to calving.
There is another reason why vaccine manufacturers need to design their products with the possibility that vaccination will occur close to calving. This reason is that typically vaccination will occur on a whole herd basis. Cows within a herd will be due to calve on different dates over a period of several weeks or months. The width of the calving span and the unpredictability of actual calving date can make it very difficult to select the ideal time to treat. For best effect, vaccines might be administered 21-35 days (according to the vaccine) prior to the earliest expected calving date within the herd or 21-35 days prior to the mean expected calving date within the herd. Some cows may calve soon after vaccination while others may calve many weeks later. Furthermore, the unpredictability of actual calving date compared to expected calving date can mean that some cows will calve much less than 21-35 days after treatment and potentially as early as the day of treatment. This short treatment to calving interval eliminates the possibility of using many anthelmintic active compounds designed to treat pregnant cows from any potential scours vaccine combination.
Vaccines containing both macrocyclic lactones and antigens, including for example peptides, membrane fractions, inactivated pathogens, and the like, are challenging to formulate due to solvent/dispersant incompatibilities. There are previous reports of combining active ingredients plus vaccines, but very few of them describe combining macrocyclic lactones plus a vaccine. One possible reason for this is that it is well known in the art that macrocyclic lactones are susceptible to degradation in the presence of other actives or in certain solvent systems, particularly aqueous solvent systems. For example, GB-A-2030043 describes injectable combinations of a non-macrocyclic lactone active (tetramisole) plus a vaccine. Importantly, the application does not disclose compositions comprising dispersing agents, which is an important component in injectable aqueous macrocyclic lactone compositions. Umehara et al report that combining one macrocyclic lactone, doramectin, with a foot-and-mouth disease vaccine may result in interference (Rev. Brasil. Parasitol. Vet., 1993, 2(2): 141-144). Other examples include JP-A-62294623, which discloses oral compositions comprising antibiotics and deactivated Salmonella, and GB-A-2267707, which describes macrocyclic lactones in optional combination with vaccination. U.S. Pat. No. 6,746,677B2 to Cobb (Wyeth, Fort-Dodge Animal Health) generally describes compositions comprising macrolide compounds or mixtures thereof, a water soluble organic solvent, a dispersing agent, an adjuvant, at least one antigen, and saline or water or a mixture thereof. In addition, patent application US 2005/0118222 A1 to Wolff describes simultaneously carrying, by means of an injection, macrocyclic lactone and an antigen against ticks. In another example, U.S. Pat. No. 6,663,879 and US U.S. Pat. No. 6,214,367 to Harvey describe stable injectable compositions that include a non-aqueous parasitic agent in a therapeutically effective amount, chosen from the group of avermectin, ivermectin, doramectin, abamectin, milbemycin and moxidectin, and an antigen in combination with a liquid carrier that also acts as an adjuvant.
The instant invention solves the problem of combining macrocyclic lactones with vaccines by using a novel and nonobvious solvent system. Unlike the alcohol solvents taught Cobb, Applicants have found that dimethyl acetamide (DMA) combined with specific surfactants provides exceptionally stable and high concentration combined macrocyclic lactone/vaccine formulations. The resulting effective dose volume is desirably lower than previous compositions.
Accordingly, there is a real and unsatisfied need in the art for a convenient means to treat pregnant cows that: protects the cow from the effects of parasitism while avoiding anthelmintic residues in milk; reduces the risk of scours in the new born calf due to viral and bacterial diseases; and provides the farmer with the ability to treat cows reasonably close to calving.